Conventionally, in the case where exteriors such as roofs and exterior walls of a building are coated with a coating film, dark-color paints have often been used in order to make dirt or the like obscure because the exteriors are easy to become dirty and are easy to observe. Pigments for use in the dark-color paints are generally carbon blacks and iron oxide blacks. However, these pigments absorb light having a wavelength ranging from an ultraviolet region to a far infrared region and therefore is easy to absorb heat rays, namely infrared rays, and thus there is a problem in these pigments that the indoor temperature of a building or car is easy to increase due to direct sunlight.
On the other hand, solar heat-reflecting paints containing a white pigment such as titanium oxide are known as paints for preventing the indoor temperature of a building from increasing, however these paints are white or light color paints and therefore are unsuitable for exteriors in many cases because dirt or the like thereon is conspicuous. Moreover, clear chromaticity is desired depending on the use application in some cases, and therefore a material for solar heat-reflecting paints or heat-reflecting paints, the material having a clear chromaticity, a dark chromatic color, or black color and having a sufficient heat-reflecting property, namely a pigment that can realize the properties has been required.
Heat-reflecting enamel in which a light-resistant vehicle, a pigment, and an extender pigment are combined, the heat-reflecting enamel useful as a heat-shielding paint for an airplane is disclosed in Patent Literature 1, and use of a titanium white-based or zinc oxide-based pigment as a white pigment, an iron oxide-based pigment or a quinacridone-based pigment as a red pigment, an iron oxide-based pigment, an iron hydroxide-based pigment, chromic acid-based pigment, or an azo-based pigment as a yellow pigment, a phthalocyanine blue-based or complex oxide-based pigment as a blue pigment, and a chrome green-based or phthalocyanine green-based pigment as a green pigment is proposed in the representative examples. However, the enamel is not preferable in terms of environmental hygiene in that the enamel contains a heavy metal such as chromium, and a solar heat-reflecting paint not using a heavy metal and having a sufficient heat-reflecting property has been awaited.
Moreover, as a new technological problem in recent years, there is an increasing number of fields seeking functional pigments having an optical property that has never been existed in generally-used conventional pigments as the progress in lasers, particularly in semiconductor lasers, and the progress of sensors thereto are made, and the development of a pigment that is applicable to these requirements is in need. In printing ink fields for example, an infrared-reflecting/transmitting pigment is required which has a function by which an ink containing an infrared-reflecting/transmitting pigment is printed and thereafter information that is unidentifiable with the naked eye can be read with an infrared reader or the like, and which can also be used effectively for printing or the like in the security fields, such as hidden bar codes, hidden two-dimensional codes, and forgery prevention of valuable papers, passports, various kinds of expert opinions in writing, and so on.